In recent years the new anthelmintic compounds of the macrolide group such as avermectins and milbemycins have been drugs of choice for the treatment of internal parasites of sheep, cattle and other farm animals. These compounds offer not only the control of many internal parasites but also external parasites and therefore have become known as endecticides. Their popularity has increased because of their dual activity and because of increasing resistance to other traditional anthelmintics like levamisole and the benzimidazoles.
However, unlike the benzimidazoles, the macrolide anthelmintics need to be administered as solutions to be bio-available as in their solid form they are poorly absorbed by the animal. It has therefore been the practice to formulate these compounds by dissolving them in solvents before administration.
Some types of parasites, particularly trematodes, that are not controlled by the macrolide endecticides. Important trematodes in sheep for example are Liver Fluke (Fasciola hepatica) and Tapeworm (Monezia spp.).
Previous methods of incorporating anthelmintics that have activity against trematodes have relied on suspending a compound like praziquantel that controls Monezia spp. in an anthelmintic solution. It is more desirable to have dual formulations as solutions as this allows wider application as injectables or drenches.